This invention relates to endoscopes suitable for magnetic resonance (MR) imaging.
Endoscopes are medical instruments suitable for insertion into a body cavity, and may include a viewing system, a light guide, an opening for injecting air or water, an opening to which a vacuum can be applied, and an opening for tools etc.
Endoscopes are usually in the form of flexible tubes which have axial passages for cables with which the tip of the endoscope may be steered, as well as for the services referred to in the preceding paragraph. In one construction, a series of outwardly-dished disks are contained in a sheath (EP-A-0 165 718).
While endoscopes produce visible images of the interior of the cavities under investigation, medical examination often requires an image of the tissue behind the tip of the endoscope. For this reason, it has been proposed to provide endoscopes with MR receive coils, in order to acquire MR signals with reasonably high signal-to-noise ratio from the tissue in the immediate vicinity of the endoscope (EP-A-0 850 595).
Such endoscopes are not at the present time commercially available, because of two principal difficulties in implementing such devices.
The first difficulty is that a conventional endoscope typically includes metals e.g. stainless steel for the steering cables, a metallic flat wire spiral for the sheath. Such materials would distort the powerful main magnetic field which underlies MR imaging, and hence the resulting MR image produced would be distorted. Secondly, currents, detrimental to the patient, would be induced in such materials when the r.f. excitation pulse, used to excite the resonance, was applied.
The second difficulty is that such an endoscope may not be fixed in position when the MR image is being built up. For example, the endoscope could be within a stomach cavity, and involuntary muscular movement of the walls could cause the endoscope to move around. An MR image requires collection of information over a period of time. For example, in order to spatially encode a two-dimensional slice, a series of r.f. excitations takes place, after each of which a phase-encode magnetic field gradient of a different magnitude is applied before a read-out pulse in the presence of an orthogonal magnetic field gradient, takes place. Any movement of the r.f. receive coil during the data collection would cause artifacts to appear in the MR image, which is calculated on the assumption that the r.f. receive coil remains fixed in position relative to the tissue during the building up of the MR image from the various pulses corresponding to the respective phase-encode gradients.
The invention provides an endoscope which includes an r.f. receive coil, wherein the tip of the endoscope which contains passages for viewing means and light guide means is made of plastics material, and wherein a bendable portion of the endoscope connected to the tip includes disks of plastics material inside a sleeve of non-metallic material, the disks having openings through which steering cables of non-metallic material pass.
Such an endoscope is MR compatible, in the sense that the materials do not interfere with the main magnetic field, nor create current inducing loops.
The tip of the endoscope may be made from polyether etherketone (PEEK). The sleeve and/or the steering cable may be made from polyethylene (for example Dyneema, made by DSM High Performance Fibers B.V., Holland, a high performance gel spun polyethylene fiber), glass, carbon, nylon (a family of polyamide polymers) or aramid (a class of aromatic polyamide fibres, such as Kevlar or Twaron).
The bendable portion of the endoscope is connected to a flexible portion, for insertion into the patient. This insertion portion may be connected by a non-metallic umbilical, of at least 2xc2xd metres, preferably at least 4 metres in length, to a services cabinet.
The invention also provides an endoscope which includes an r.f. receive coil, and a fiducial fixed relative to the r.f. receive coil which is provided with its own r.f. receive coil.
It then becomes possible to track the movement of the r.f. receive coil so that movement of the r.f. receive coil can be compensated for when building up the MR image.